A method for converting high-silicon molten iron in a converter

Abstract

The application discloses a method for converter blowing high-silicon molten iron, wherein when the silicon content in the molten iron is less than or equal to 1.00%, the slag basicity of the first tapping is controlled to be 1.4-1.8; when the silicon content in the molten iron is greater than 1.00%, the slag basicity of the first tapping is controlled to be 0.9-1.3; and the lime addition amount after double-slagging is determined by using formula (I). The method can ensure the amount of the first slag, control splashing after the first slagging, reduce the amount of slag added after the first slagging, and ensure the dephosphorization rate at the end point, thereby making the blowing of the high-silicon molten iron more smooth, reducing the cost of the slag, and increasing the hit rate at the end point. The method can improve the dephosphorization efficiency and the primary carbon extraction rate of the converter blowing high-silicon molten iron by reasonably controlling the initial slag basicity; different initial slag basicities are determined according to different silicon contents in the molten iron, thereby further reducing the consumption of the slag such as lime during the converter blowing of the high-silicon molten iron, reducing the slag cost per ton of steel, and reducing the consumption cost of the slag such as lime during the smelting process of the high-silicon molten iron under the premise of inhibiting splashing and ensuring the dephosphorization effect.

Description

Technical Field

[0001] This invention relates to a converter smelting method, and more particularly to a converter blowing method for producing high-silicon molten iron. Background Technology

[0002] Most steel plants require double-slag / multi-slag operation when the silicon content of molten iron is >0.60%, such as the converter workshop of Xinggang Steel Plant. Previously, the silicon content of high-silicon molten iron was generally in the range of 0.60-0.90%, and the basicity of the slag in the first pour was controlled to be in the range of 2.0-2.5 for molten iron with silicon content in the range of 0.90-1.2% (the highest range of molten iron considered when the plan was written). The quality plan stipulates that the ash consumption should be controlled at 60-66 kg / t when the silicon content of molten iron is 0.90-1.2%, and there is no clear standard for the control range of the basicity of the initial slag.

[0003] To consume high-silicon molten iron without affecting output, the converter process implements a single furnace stand for consuming high-silicon molten iron. In order to achieve normal dephosphorization and splash control during the high-silicon molten iron blowing process in a single converter, a double-slag / multi-slag process is adopted in the converter. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for converter blowing high-silicon molten iron while ensuring dephosphorization effect and reducing slag addition.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: when the silicon content in the molten iron is ≤1.00%, the basicity of the first-turn slag is controlled at 1.4 to 1.8; when the silicon content in the molten iron is >1.00%, the basicity of the first-turn slag is controlled at 0.9 to 1.3; the amount of lime added after the double slag process is determined by the following formula (Ⅰ).

[0006]

[0007] In formula (Ⅰ): R1 is the basicity of the slag after the first pour; R2 is the basicity of the slag at the end of the blowing process; k is the slag pouring coefficient, which is taken as 0.5 to 0.7 in the preliminary calculation and can be adjusted according to the actual slag pouring amount or the recalculated value; m1 is the amount of lime added before the first pour, kg; m2 is the amount of lime added after the first pour, kg; t is the amount of molten iron charged, kg; ω Si Silicon content in molten iron, %; ω CaO CaO content in lime, %; ω SiO2 The SiO2 content in lime, in percentages.

[0008] Furthermore, the target basicity of the final slag from the converter blowing process is 3 to 4.

[0009] The beneficial effects of adopting the above technical solution are as follows: Under the control range of initial slag basicity, this invention can ensure the amount of slag poured during the first pour, which plays a good role in controlling splashing after slag pouring, reducing the amount of slag added after slag pouring, and ensuring the final dephosphorization rate, making the high-silicon molten iron blowing process smoother; the slag cost is lower, and the final hit rate is higher (increasing the first-pass carbon removal rate of the converter). This invention improves the dephosphorization efficiency and first-pass carbon removal rate of converter blowing of high-silicon molten iron by reasonably controlling the initial slag basicity; different initial slag basicities are determined according to different silicon contents of molten iron, further reducing the consumption of lime and other slag materials during converter blowing of high-silicon molten iron, and reducing the slag cost per ton of steel; while achieving the goal of suppressing splashing and ensuring the dephosphorization effect, the consumption cost of lime and other slag materials in the high-silicon molten iron smelting process is reduced. Attached Figure Description

[0010] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0011] Figure 1 This is a schematic diagram showing the relationship between the dephosphorization rate and the basicity of the slag in the converter blowing process for high-silicon molten iron described in this invention.

[0012] Figure 2 This is a schematic diagram showing the relationship between silicon content in molten iron and basicity in the first-turn slag during the converter blowing process for high-silicon molten iron as described in this invention. Detailed Implementation

[0013] The method for producing high-silicon molten iron in this converter adopts the following process steps: 1) Selection of initial slag basicity for different silicon ranges in molten iron:

[0014] The so-called initial slag basicity refers to the "first-turn slag basicity" described in this method, which is the basicity of the slag in the early stage of blowing high-silicon molten iron, when the CO reaction begins and slag is raised in the furnace as the furnace temperature rises. In terms of slag raising time, the oxygen supply time before the first turn of slag is generally distributed in the range of 200-260s, and in some furnaces with low molten iron temperature and poor slag melting, the oxygen supply time reaches 350-380s during slag raising.

[0015] This method controls the basicity of the first-turn slag at 1.4–1.8 when the silicon content of molten iron is 0.70% ≤ Si ≤ 1.00 wt%; and controls the basicity of the first-turn slag at 0.9–1.3 when the silicon content of molten iron is > 1.00 wt%. The basicity is controlled from the lower limit of the high silicon content range to the upper limit of the low silicon content range. The silicon content in the molten iron refers to the silicon content of the blast furnace molten iron entering the converter. When slag formation begins in the CO reactor (i.e., during the first turn), the silicon content in the molten iron will be basically oxidized. The target basicity of the final slag is 3–4. The basicity of the first-turn slag and the final slag are best controlled as shown in Table 1.

[0016] Table 1: Optimal Basicity of First-Turn Slag and Target Final Slag Basicity

[0017]

[0018]

[0019] Figure 1 As shown, the dephosphorization rate of the first pour is directly proportional to the basicity of the slag in the first pour. However, due to the limited oxygen supply time before the first pour, the amount of slag required to achieve the same basicity of slag increases significantly with the increase of silicon content in the molten iron. If the effect of basicity on dephosphorization is pursued blindly, it will result in the slag not melting during the first pour and a small amount of slag being poured out, which will lead to insufficient basicity of the final slag in the converter, reduce the final dephosphorization rate, and increase slag consumption.

[0020] Figure 2 As shown, if the amount of lime added before pouring (the amount of limestone added is approximately multiplied by 0.5 to convert it into the amount of lime added) is too small, the slag will be thin and cannot be poured down into the furnace after the lance is lifted. After the furnace is leveled, the slag will not foam and the amount of slag poured will be small, which will also make it difficult to guarantee the dephosphorization effect of the entire blowing process. Under the premise of ensuring the final phosphorus hit requirement P≤0.020%, the basicity of the molten iron silicon is 0.70%≤Si≤1.00wt%, and the basicity of the first-turn slag is distributed in the range of 1.4 to 1.8. When the molten iron silicon is higher than 1.00%, the basicity of the first-turn slag is distributed in the range of 0.9 to 1.3. Overall, as the molten iron silicon increases, the basicity of the first-turn slag shows a significant decreasing trend. After the molten iron silicon content increases to 1.9%, the basicity of the first-turn slag is basically controlled at around 0.9. Under the above-mentioned initial slag basicity control range, the amount of slag dumped during the first turn can be guaranteed. This plays a good role in controlling splashing after dumping, reducing the amount of slag added after dumping, and ensuring the final dephosphorization rate. This makes the high-silicon molten iron blowing smoother, lower in cost, and higher in endpoint hit rate (increasing the first-time carbon removal rate of the converter).

[0021] 2) Method for determining the amount of alkaline slag materials such as lime added after double slag addition:

[0022] The amount of lime added after the double slag process is determined by the following formula (Ⅰ);

[0023]

[0024] In formula (Ⅰ): R1 is the basicity of the first slag pour; R2 is the basicity of the slag at the blowing end; k is the slag pouring coefficient, which is taken as 0.5 to 0.7 in the preliminary calculation and can be adjusted according to the actual slag pouring or the recalculated value. The range after recalculation adjustment is generally 0.33 to 0.76; m1 is the amount of lime added before the first slag pour, i.e., the amount of lime added before the first slag pour, kg; m2 is the amount of lime added after the first slag pour, i.e., the amount of lime added after the first slag pour, kg; t is the amount of molten iron charged, kg; ω Si Silicon content in molten iron, wt%; ω CaO The CaO content in lime, wt%; ω SiO2The SiO2 content in the lime is expressed in wt%. If limestone or a mixture of lime and limestone is added before and / or after the first pour, the amount of limestone added is approximately multiplied by 0.5 to convert it into the amount of lime added. Since the amount of dolomite / lightly calcined dolomite added is fixed according to different steel grades, its impact on the overall basicity is low under high-silicon molten iron conditions and is therefore ignored in the calculation.

[0025] Limestone serves as both a slag-forming material and a coolant. If there is still excess temperature, iron-containing coolants such as sinter can be used to adjust the temperature, keeping the semi-steel temperature ≤1500℃ during the first slag dumping. The amount of lime / limestone added from the start of blowing to the first slag dumping can be determined by selecting the initial slag basicity according to the initial slag basicity determination principle in step 1) above, given the actual known silicon content of the molten iron. Then, it can be obtained using the binary slag basicity calculation formula.

[0026] According to formula (Ⅰ): the alkalinity of the initial slag and the alkalinity of the final slag are known, the amount of lime / limestone added before and after the double slag is known, and the slag dumping coefficient is taken as 0.5 to 0.7 for pre-calculation. If the final slag cannot meet the requirements or the final phosphorus is high, the actual k value of the shift can be recalculated by taking another sample, and then the k value of the current furnace can be corrected. According to the actual test of the slag alkalinity, the slag dumping coefficient of the first dump is distributed between 0.33 and 0.76 (average 0.56). The slag dumping coefficient is directly proportional to the final dephosphorization rate. If the amount of slag dumped in the first dump is significantly less, the lance operator should increase the amount of lime added after the first dump accordingly, or perform three-slag / multi-slag operation according to the subsequent slag splashing situation.

[0027] Within the limit of the furnace shaking angle, pour out as much initial slag as possible. The furnace shaking angle limit can be appropriately increased according to the ash consumption requirements and the final phosphorus content. However, it should be noted that there are more iron beads in the initial slag, and the amount of slag poured out should also take into account the consumption of steel materials.

[0028] 3) Prior to this invention, in the process of blowing high-silicon molten iron in Xinggang converter, the basicity of the initial slag of high-silicon molten iron was controlled at 2.0 to 2.5. This method, through the determination and standardized implementation of the above-mentioned initial slag basicity, increases the carbon removal rate of the converter in the smelting of high-silicon molten iron by at least 15% and reduces ash consumption by more than 10 kg / t, with significant effects.

[0029] Example 1: The specific method for blowing high-silicon molten iron in this converter is as follows.

[0030] 1) The steel grade being smelted is XGML40Cr. The oxygen supply time before the first slag pour is 204s, the silicon content of the molten iron entering the furnace is 0.715%, the basicity of the first slag pour is controlled at 1.8, the slag pouring coefficient is 0.5, and the final slag basicity is 3.5.

[0031] 2) The amount of lime added from the start of blowing to the first slag dumping is 1423 kg, and the amount of limestone added is 1958 kg. The temperature of the semi-steel during the first slag dumping is controlled at ≤1500℃, the lime CaO content is 88%, the SiO2 content is 1.5%, and the initial slag basicity is controlled at 1.8. The amount of lime added in the first dumping = 1000 × iron volume (t) × iron silicon (%) × 2.14 ÷ effective CaO (%) = 1000 × 74.05 × 0.715% × 2.14 × 1.8 ÷ (88% - 1.8 × 1.5%) ≈ 2391 kg (actually 2402 kg added).

[0032] The amount of lime added after the first pour is calculated using formula (Ⅰ): Amount of lime added after the first pour = (1-0.5)×(2.14×74.05×1000×0.715%+2402×1.5%)×(3.5-1.8)÷(88%-3.5×1.5%), which calculates to 1201kg of lime added after the first pour (actually 1064kg of lime and 306kg of limestone were added).

[0033] 3) After adopting the above process, the carbon extraction rate is 86.7% and the ash consumption is 45.6 kg / t (calculated as limestone addition amount ÷ 2).

[0034] Example 2: The specific method for blowing high-silicon molten iron in this converter is as follows.

[0035] 1) The steel grade being smelted is 10B21. The oxygen supply time before the first slag pour is 228s, the silicon content of the molten iron entering the furnace is 0.876%, the basicity of the first slag pour is controlled at 1.6, the slag pouring coefficient is 0.7, and the final slag basicity is 3.1.

[0036] 2) The amount of lime added from the start of blowing to the first slag dumping is 1137 kg, and the amount of limestone added is 832 kg. The temperature of the semi-steel during the first slag dumping is controlled at ≤1500℃, the lime CaO content is 88%, the SiO2 content is 1.5%, and the initial slag basicity is controlled at 1.6. The amount of lime added in the first dumping = 1000 × iron volume (t) × iron silicon (%) × 2.14 ÷ effective CaO (%) = 1000 × 44 × 0.876% × 2.14 × 1.6 ÷ (88% - 1.6 × 1.5%) ≈ 1542 kg (actually 1553 kg was added).

[0037] The amount of lime added after the first pour is calculated using formula (Ⅰ): Amount of lime added after the first pour = (1-0.7)×(2.14×44×1000×0.876%+1553×1.5%)×(3.1-1.6)÷(88%-3.1×1.5%), which calculates to 458kg of lime added after the first pour (439kg was actually added).

[0038] 3) After adopting the above process, the carbon extraction rate is 81.0% and the ash consumption is 41.9 kg / t (calculated as limestone addition amount ÷ 2).

[0039] Example 3: The specific method for blowing high-silicon molten iron in this converter is as follows.

[0040] 1) The steel grade smelted is SWRCH22A. The oxygen supply time before the first slag pour is 236s, the silicon content of the molten iron entering the furnace is 0.984%, the basicity of the first slag pour is controlled at 1.4, the slag pouring coefficient is 0.7, and the final slag basicity is 3.1.

[0041] 2) The amount of lime added from the start of blowing to the first slag dumping is 1211 kg and the amount of limestone added is 582 kg. The temperature of the semi-steel during the first slag dumping is controlled at ≤1500℃, the lime CaO content is 88% and the SiO2 content is 1.5%, and the initial slag basicity is controlled at 1.4. The amount of lime added in the first dumping = 1000 × iron volume (t) × iron silicon (%) × 2.14 ÷ available CaO (%) = 1000 × 43.9 × 0.984% × 2.14 × 1.4 ÷ (88% - 1.4 × 1.5%) ≈ 1507 kg (actually 1502 kg was added).

[0042] The amount of lime added after the first pour is calculated using formula (Ⅰ): Amount of lime added after the first pour = (1-0.7)×(2.14×43.9×1000×0.984%+1502×1.5%)×(3.1-1.4)÷(88%-3.1×1.5%), which calculates to be 579kg of lime added after the first pour (actually 568kg was added).

[0043] 3) After adopting the above process, the carbon extraction rate is 90% and the ash consumption is 45.1 kg / t (calculated as limestone addition amount ÷ 2).

[0044] Example 4: The specific method for blowing high-silicon molten iron in this converter is as follows.

[0045] 1) The steel grade smelted is ML20MnTiB. The oxygen supply time before the first slag pour is 233s, the silicon content of the molten iron entering the furnace is 1.204%, the basicity of the first slag pour is controlled at 1.3, the slag pouring coefficient is 0.7, and the final slag basicity is 3.3.

[0046] 2) The amount of lime added from the start of blowing to the first slag dumping is 618 kg, and the amount of limestone added is 2260 kg. The semi-steel temperature during the first slag dumping is controlled at ≤1500℃, the lime CaO content is 88%, and the SiO2 content is 1.5%. The initial slag basicity is controlled at 1.3. The amount of lime added in the first dumping = 1000 × molten iron quantity (t) × molten iron silicon (%) × 2.14 ÷ available CaO (%) = 1000 × 45 × 1.204% × 2.14 × 1.3 ÷ (88% - 1.3 × 1.5%) ≈ 1752 kg. (Actual amount added: 1748 kg)

[0047] The amount of lime added after the first pour is calculated using formula (Ⅰ): Amount of lime added after the first pour = (1-0.7)×(2.14×45×1000×1.204%+1748×1.5%)×(3.3-1.3)÷(88%-3.3×1.5%), which calculates to 857kg of lime added after the first pour (actually 863kg was added).

[0048] 3) After adopting the above process, the carbon extraction rate is 83.3% and the ash consumption is 55.8 kg / t (calculated as limestone addition amount ÷ 2).

[0049] Example 5: The specific method for blowing high-silicon molten iron in this converter is as follows.

[0050] 1) The steel grade smelted is SWRCH10A. The oxygen supply time before the first slag pour is 299s, the silicon content of the molten iron entering the furnace is 1.478%, the basicity of the first slag pour is controlled at 1.2, the slag pouring coefficient is 0.65, and the final slag basicity is 3.0.

[0051] 2) The amount of lime added from the start of blowing to the first slag dumping is 965 kg, and the amount of limestone added is 2064 kg. The temperature of the semi-steel during the first slag dumping is controlled at ≤1500℃, the lime CaO content is 88%, the SiO2 content is 1.5%, and the initial slag basicity is controlled at 1.2. The amount of lime added in the first dumping = 1000 × iron volume (t) × iron silicon (%) × 2.14 ÷ effective CaO (%) = 1000 × 45.5 × 1.478% × 2.14 × 1.2 ÷ (88% - 1.2 × 1.5%) ≈ 2003 kg (actually 1997 kg was added).

[0052] The amount of lime added after the first pour is calculated using formula (Ⅰ): Amount of lime added after the first pour = (1-0.65)×(2.14×45.5×1000×1.478%+1997×1.5%)×(3.0-1.2)÷(88%-3.0×1.5%), which calculates to 1108kg of lime added after the first pour (actually 880kg of lime and 401kg of limestone were added).

[0053] 3) After adopting the above process, the carbon extraction rate is 71.4% and the ash consumption is 64.2 kg / t (calculated as limestone addition amount ÷ 2).

[0054] Example 6: The specific method for blowing high-silicon molten iron in this converter is as follows.

[0055] 1) The steel grade being smelted is SWRCH35K. The oxygen supply time before the first slag pour is 305s, the silicon content of the molten iron entering the furnace is 1.758%, the basicity of the first slag pour is controlled at 1.0, the slag pouring coefficient is 0.65, and the final slag basicity is 3.0.

[0056] 2) The amount of lime added from the start of blowing to the first slag dumping is 946 kg, and the amount of limestone added is 1486 kg. The temperature of the semi-steel during the first slag dumping is controlled at ≤1500℃, the lime CaO content is 88%, the SiO2 content is 1.5%, and the initial slag basicity is controlled at 1.0. The amount of lime added in the first dumping = 1000 × iron volume (t) × iron silicon (%) × 2.14 ÷ effective CaO (%) = 1000 × 39 × 1.758% × 2.14 × 1.0 ÷ (88% - 1.0 × 1.5%) ≈ 1696 kg (actually 1689 kg was added).

[0057] The amount of lime added after the first pour is calculated using formula (Ⅰ): Amount of lime added after the first pour = (1-0.65)×(2.14×39×1000×1.758%+1689×1.5%)×(3.0-1.0)÷(88%-3.0×1.5%), which calculates to be 1251kg of lime added after the first pour (actually 1122kg of lime and 307kg of limestone were added).

[0058] 3) After adopting the above process, the carbon extraction rate is 66.7% and the ash consumption is 60.2 kg / t (calculated as limestone addition amount ÷ 2).

[0059] Example 7: The specific method for blowing high-silicon molten iron in this converter is as follows.

[0060] 1) The steel grade being smelted is XGSWRCH45K. The oxygen supply time before the first slag pour is 313s, the silicon content of the molten iron entering the furnace is 2.181%, the basicity of the first slag pour is controlled at 0.9, the slag pouring coefficient is 0.75, and the final slag basicity is 2.8.

[0061] 2) The amount of lime added from the start of blowing to the first slag dumping is 1733 kg, and the amount of limestone added is 3345 kg. The temperature of the semi-steel during the first slag dumping is controlled at ≤1500℃, the lime CaO content is 88%, the SiO2 content is 1.5%, and the initial slag basicity is controlled at 0.9. The amount of lime added in the first dumping = 1000 × iron volume (t) × iron silicon (%) × 2.14 ÷ effective CaO (%) = 1000 × 70 × 2.181% × 2.14 × 0.9 ÷ (88% - 0.9 × 1.5%) ≈ 3393 kg (actually 3406 kg was added).

[0062] The amount of lime added after the first pour is calculated using formula (Ⅰ): Amount of lime added after the first pour = (1-0.75)×(2.14×70×1000×2.181%+3406×1.5%)×(3.0-0.9)÷(88%-3.0×1.5%), which calculates to be 2086kg of lime added after the first pour (actually 1457kg of lime and 1016kg of limestone were added).

[0063] 3) After adopting the above process, the carbon extraction rate is 58.3% and the ash consumption is 66.0 kg / t (calculated as limestone addition amount ÷ 2).

Claims

1. A method for converter blowing high-silicon molten iron, characterized in that: When the silicon content in the molten iron is ≤1.00%, the basicity of the first-turn slag is controlled at 1.4–1.8; when the silicon content in the molten iron is >1.00%, the basicity of the first-turn slag is controlled at 0.9–1.3; the amount of lime added after the double slag process is determined by the following formula (Ⅰ). （Ⅰ） In formula (Ⅰ): R1 is the basicity of the first slag pour; R2 is the basicity of the final slag at the end of blowing; k is the slag pouring coefficient, which is taken as 0.5 to 0.7 in the preliminary calculation and can be adjusted according to the back calculation value; m1 is the amount of lime added before the first pour, kg; m2 is the amount of lime added after the first pour, kg; t is the amount of molten iron charged, kg; ω Si The silicon content in molten iron, %; ω CaO The CaO content in lime, %; ω SiO2 The SiO2 content in lime, % The target basicity of the final slag from the converter blowing process is 3 to 4.

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